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NDT Methods Applicable to Health Monitoring of ABC Closure Joints

Regardless of the fabrication and installation methods of precast-prefabricated elements, connections among these elements need to be established on site and in place. These connections, Closure Joints, are expected to provide continuity between adjoining elements for the purpose they are designed for. Therefore, normally, they contain reinforcing bars and enclosures of various shapes that in some cases create congestion within the joint. To provide shear connectivity, some of these joints are designed with cavities within the precast elements. In all, the specific nature of the joint application, in-situ casting, curing, material incompatibility, cavities and steel congestion contribute to creating potential for leaving defects and anomalies in the closure joints. This, in turn, results in a higher potential for exposure and other detrimental effects with possible degradation in time, and therefore reducing the strength and serviceability of the joint and the structure. The long-term deflections and environmental loading will only exacerbate the situation. It is therefore critical to first assure the closure joint is in good health right after construction completes, and secondly to remain healthy in future.
A variety of Non-Destructive Testing (NDT) methods have been utilized for evaluation of bridges including those with closure joints. However, a concerted attempt for categorization of these methods, comparison of capabilities, and selection of methods most applicable to closure joints is lacking. The presence of defects may be readily identifiable by detecting significant anomalies in the response of the joint to NDT techniques. However, the overall approach to NDT evaluation of closure joints will also include constructing a signature response record of an intact joint to specific NDT technique at completion of construction. This base record will be used for comparison with future periodic (or on demand) inspections for determining the type and extent of potential damages.
In conjunction with review of various NDT methods, it is the intent of this project to evaluate the promising NDT techniques, and identify how best these techniques could be used to provide suitable practical methods for health monitoring of the accelerated bridge construction (ABC) structure. It will be attempted to organize the project results in a manner to allow, in a separate follow-up project, development of field procedures, evaluation guidelines, and reporting methods and appraisal of methods for ease of use and suitability for integration into states bridge inspection programs. The study will also aim at identifying details, damage types, and closure types for which suitable methods may not exist at present, and recommend alternate ideas.